Multi-spindle machines, also referred to as multiple spindle machines, are known in the prior art. Multi-spindle machines are used to mass produce standardized types of components. A multi-spindle machine typically has several work stations at which machining operations are performed. A piece of raw stock, such as bar stock, enters the machine at a first station and as the machine indexes, various machining operations are performed. Once this station is indexed completely through the machine, a completed part is formed. The part is released, and the process is repeated for that station with a new piece of raw stock. An advantage of multi-spindle machines is that all stations in the machine are producing parts simultaneously, resulting in high production.
Multi-spindle machines typically have a large indexing or main drum with four, five, six or eight stations thereon. Each of the stations carries a work piece. In all but one of the stations, where a new piece of stock enters, a machining operation is performed. After each operation is completed, the drum is rotated so that each work piece moves sequentially through the location where the various operations are performed. The machining operations typically performed in a multi-spindle machine include milling, turning, and threading.
While multi-spindle machines are very efficient in terms of producing standardized parts at a high rate they also have drawbacks. The primary drawback associated with multi-spindle machines is that the entire machine operates off of a single main motor. The main motor through a series of interconnecting shafts and gears drives all of the devices within the machine. All of these devices perform their operations simultaneously during a low speed and a high speed operation. Multi-spindle machines typically include a timing shaft for the coordination of multiple machine operations and proper speed. The operator of the machine is still required to set up the cams operating off the timing shaft which can be a very time consuming activity.
There is always a risk that one of the mechanisms within the machine will malfunction. If such a malfunction should occur and not be detected by an operator in time to shut the machine off, the machine will continue with its next cycle. In many cases an attempt by the machine to index to its next position will cause severe damage. This is why it is common for a human operator to be required to closely monitor multi-spindle machines.
Another drawback associated with multi-spindle machines is that typically the machines must change from high to low speed and back again during the course of their operating cycle. High speed is typically used for times in the machine cycle when critical machining operations are not occurring. High speed operation is desirable when the stations are indexing or when the tools are moving toward or away from the work pieces. Low speed operation is used when the tools in the machine are forming the metal or performing work on the work pieces at a station. Any attempt to operate the machine in high speed when such forming work is being performed is likely to cause a problem or possibly jam the machine.
It is the responsibility of the operator or technician to set the points in the machine cycle where the machine makes its high speed and low speed shifts. Shifting from high to low speed too early may result in slower cycle times and production rates. The same result may occur if the shift from low to high speed is made too late. The fastest cycle time for multi-spindle machines has been about 0.8 seconds. Use of the embodiments of the present invention can reduce that time to about 0.6 seconds.
Co-pending U.S. patent application Ser. No. 08/871,019 titled Multi-Spindle Machine Retrofit System filed on Jun. 6, 1997 is directed to a control system for a multi-spindle machine. It is assigned to the Assignee of the present invention and hereby incorporated by reference. The system disclosed therein decreases the cycle time, minimizes wear on the drive train gears, and enables a more effective operation of the multi-spindle machine by providing a retrofit system which includes a brake clutch, a feed clutch, and a high speed clutch. These three clutches are incorporated into the drive train gear layout of the multi-spindle machine and are pneumatically actuated and electronically controlled.
Another patent application also assigned to the Assignee of the present invention was co-pending with the Provisional U.S. Patent Application from which this application claims priority. That application is titled Multi-Spindle Machine Control System, U.S. patent application Ser. No. 08/423,238 filed on Apr. 17, 1995, issued as U.S. Pat. No. 5,730,037 on Mar. 24, 1998 and its contents are hereby incorporated by reference. U.S. Pat. No. 5,730,037 describes a control system for a multi-spindle machine that increases productivity, minimizes down time, and enables the more effective operation and monitoring of production by providing a controller on each side of the multi-spindle machine. The controller provides an interface with an administrative work station as well as including a user interface with display and key pad. The controller is in communication with a number of sensors mounted on the machine. In the event of a failure or a fault condition, the sensors detecting such fault or failure operatively through the controller shut down the main motor to prevent further damage and at the same time display the cause of the malfunction.
Still another related application is titled Threading Clutch and describes a threading clutch with biasing means situated between the friction disks. It is application Ser. No. 08/992,773 and was filed on Dec. 17, 1997 and is also hereby incorporated by reference.
U.S. Pat. No. 4,644,819 describes a high-low speed drive system for multiple spindle machines employing selective engagement and disengagement of associated pneumatic operated disc clutches.
The ball type threading clutch is a mechanical threading clutch typically employed on a multi-spindle machine, for example a Davenport 5 Spindle Automatic Screw Machine Model B. The ball type threading clutch replaced the wedge type formerly employed in this application since the ball type threading clutch shifts much easier than the wedge type. The ball type threading clutch requires the use of a torque wrench on the threading spindle. Each side of the clutch is mechanically adjusted to between about 20-25 foot pounds (ft. lbs.) when cold and a torque of about 35 foot pounds when warmed up. A specific problem with misadjustment of a threading clutch is a "bucking" which can strip the nylon gears of a Davenport Model B. Another problem with this type of mechanical threading clutch is that the torque capacity is not consistent during the warm up period. There is about a 10-15 foot pound differential in tap torque and an inconsistent tap depth. The tap depth adjustment requires a mechanical turnbuckle screw thread type adjustment. This "hit and miss" approach presents problems for the operators.
Thus, there exists a need for an improved threading clutch with a control system for a multi-spindle machine, and particularly those of a Davenport Model B construction, that eliminates the mechanical screw thread type clutch adjustment. Preferably, such an improved threading clutch would allow for torque adjustment pneumatically with the ability of varying the static torque capacity with the air pressure. Also, the improved threading clutch would achieve coarse tap depth adjustment by movement of an electrical trip switch device. The fine tap adjustment would be achieved electronically with a timer relay.